The invention relates to an apparatus for carrying out membrane separation processes, comprising a housing, at least one spirally wound-up membrane pocket arranged within the housing and containing at least one drainage layer and semipermeable membranes applied to both sides thereof, a spacer between the individual wound plies of the membrane pocket, a centrally arranged collection line, a first end-face opening as an inlet for the material to be separated, a second end-face opening as an outlet for the concentrate and a discharge line for the permeate which has passed into the collection line.
Such types of apparatus, which are in general called membrane modules, are known in the literature and are described in the most diverse embodiments for various applications (see, for example Ullmann, Enzyklopdieder technischen Chemie, [Encyclopedia of Industrial Chemistry], 4th edition, volume 2, page 188). In the case of the spirally wound-up membrane elements, however, there are known problems, in particular with respect to the sealing of the membrane elements in the side regions or in the region of the inlet to the collection line (Ullmann).
DE-A-3,033,800 describes that, for solving these sealing problems, the membranes forming the wound membrane element should be mutually joined by adhesives in the regions adjacent to the side edge. However, the use of adhesive, when carrying out membrane separation processes, sometimes leads to far-reaching problems, in particular in operation or in cleaning of the membrane elements at higher temperatures and/or with organic solvents. There are problems also in types of apparatus where economical utilization of the total membrane surface is important and when carrying out separation processes in connection with foodstuffs or luxury foods intended for consumption.